Solid golf ball

Details Solid golf ball Solid golf ball

1999-12-20

2001-08-07

Buttner, David J. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C473S373000, C473S374000, C473S376000

Reexamination Certificate

active

06271296

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a golf ball of four or multilayer structure offering pleasant feel when hit, improved durability, and increased distance.
2. Prior Art
A variety of multi-piece golf balls including three-piece and four-piece ball constructions have been developed over the past few years in order to improve ball performance. The practice is known of balancing a soft feel with good resilience in multi-piece golf balls by giving the ball a hardness distribution across its respective layers (core, intermediate layer and cover) in such a way as to retain both properties. In particular, a number of patents have been described on techniques for softening the core in order to achieve a soft feel (see, for example, JP-B 4-55077, JP 2674627, and JP-A 7-194735).
The cores of the golf balls disclosed in these patents all have a diameter of about 30 mm, or at least about 20 mm. Softening the core significantly lowers its resilience, which must then be compensated for by increasing the hardness of the intermediate layer and cover, to provide a reasonable resilience for the ball as a whole. However, increasing the hardness of these layers gives the ball a poor feel. In addition, stress concentration due to differences in hardness arises at the interface between the soft core and the hard intermediate layer, causing the layers to separate. JP-A 11-417 discloses a core provided with an inner layer of relatively small diameter. Yet, here too, there exists a large difference in hardness between the inner layer and the intermediate layer that has been formed around and encloses the inner layer, resulting in interfacial adhesion problems such as interlayer separation, and poor durability due to rubber fissuring in the intermediate layer.
SUMMARY OF THE INVENTION
An object of the invention is to provide a solid golf ball of four or multilayer structure offering pleasant feel when hit, improved durability, and increased distance.
According to the invention, there is provided a solid golf ball of four or multilayer structure comprising a core, an enclosing layer around the core, an intermediate layer around the enclosing layer, and a cover around the intermediate layer. The core is comprised of a thermoplastic resin or thermoplastic elastomer as a base and has a diameter of 3 to 18 mm and a Shore D hardness of 15 to 50. The enclosing layer is comprised of a thermoplastic resin or thermoplastic elastomer as a base. The enclosing layer and the intermediate layer have a substantially equal Shore D hardness at a boundary therebetween.
The intermediate layer may be formed of a rubber composition comprising polybutadiene as a base. Preferably, the Shore D hardness of the core is lower than that of the intermediate layer. The core may have a specific gravity of at least 1.10.
The invention is directed to a solid golf ball of multilayer structure comprising at least four layers: a core, an enclosing layer, an intermediate layer, and a cover. It has been found that when the core is formed primarily of a thermoplastic resin or thermoplastic elastomer to a diameter of 3 to 18 mm and a Shore D hardness of 15 to 50, the enclosing layer is formed primarily of a thermoplastic resin or thermoplastic elastomer, and the enclosing layer and the intermediate layer have a substantially equal Shore D hardness at a boundary therebetween, the golf ball becomes durable against strikes and offers pleasant feel and travels good distance when hit.
As opposed to the conventional use of rubber compositions such as polybutadiene as the core material, the invention selects a resinous material and a small diameter for the core. Using a resin material in the core greatly facilitates the grinding step, making it possible to efficiently produce small-diameter cores. Moreover, the decline in the resilience due to the use of a resin material in the core is relatively small for the ball as a whole because of the small diameter of the core. The problem of interfacial separation is substantially eliminated since the enclosing layer and the intermediate layer are substantially equal in hardness.


REFERENCES:
patent: 5779562 (1998-07-01), Melvin
patent: 6071201 (2000-06-01), Maruko

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